E-cigarette puffing patterns associated with high and low nicotine e-liquid strength: effects on toxicant and carcinogen exposure

Symptoms of nicotine dependence by e-cigarette and cigarette use behavior and brand: A population-based, nationally representative cross-sectional study

BACKGROUND

Many modern e-cigarette brands contain equivalent or higher nicotine levels than traditional cigarettes.

OBJECTIVE

To examine differences in four nicotine dependence indicators (i.e., use within 30minutes of waking, cravings, needing to use, and frequent use) among adolescents (aged 12-17 years) with past 30-day (P30D) exclusive use of e-cigarettes, cigarettes, or dual use of both.

METHODS

Data were from Wave 5 (2018-2019) of the Population Assessment of Tobacco and Health (PATH) study (n=1060; N=2053,659). Multivariable logistic regression was performed to determine differences in indicators by P30D e-cigarette and cigarette use behavior (exclusive vs. dual use) and brand (e-cigarette use: JUUL vs. non-JUUL vs. Unknown).

RESULTS

The odds of frequent use among adolescents with JUUL (AOR: 2.11; 95% CI=1.02-4.37) and non-JUUL (AOR: 2.12; 95% CI=0.95-4.77) use were similar and paralleled that for dual use (AOR: 3.50; 95% CI=1.46-8.43) but were stronger (JUUL only) than exclusive cigarette use. The odds of using within 30minutes of waking for adolescents with JUUL (AOR: 2.23; 95% CI=0.80-6.25) and non-JUUL (AOR:1.42; 95% CI=0.47-4.32) use were similar and paralleled that for both dual (AOR=3.00; 95% CI=1.01-8.88) and exclusive cigarette use. For adolescents who used unknown brands, the odds of all indicators paralleled exclusive cigarette use but were lower than JUUL, non-JUUL, and dual use.

CONCLUSION

Compared to exclusive cigarette use, symptoms of nicotine dependence are similar for adolescents with exclusive e-cigarette use, irrespective of brand. Symptoms of nicotine dependence for JUUL and non-JUUL use parallel dual use. Tobacco regulation should consider these findings when assessing the abuse liability of e-cigarettes.

Increased oxidative stress responses in murine macrophages exposed at the air-liquid interface to third- and fourth-generation electronic nicotine delivery system (ENDS) aerosols

Background

New fourth generation electronic nicotine delivery system (ENDS) devices contain high levels of nicotine salt (up to 60 mg/mL), whose cellular and molecular effects on immune cells are currently unknown. Here, we used a physiologically-relevant in vitro air-liquid interface (ALI) exposure model to assess the toxicity of distinct ENDS, a 3rd-generation electronic-cigarette (e-cig) and two 4th-generation ENDS devices (JUUL and Posh Plus).

Methods

Murine macrophages (RAW 264.7) were exposed at the ALI to either air, Menthol or Crème Brûlée-flavored ENDS aerosols generated from those devices for 1-hour per day for 1 or 3 consecutive days. Cellular and molecular toxicity was evaluated 24 h post-exposure.

Results

1-day of Menthol-flavored JUUL aerosol exposure significantly decreased cell viability and significantly increased lactate dehydrogenase (LDH) levels compared to air controls. Further, JUUL Menthol elicited significantly increased reactive oxygen species (ROS) and nitric oxide (NO) production compared to air controls. Posh Crème Brûlée-flavored aerosols displayed significant cytotoxicity - decreased cell viability and increased LDH levels -after 1- and 3-day exposures, while the Crème Brûlée-flavored aerosol produced by the 3rd-generation e-cig device only displayed significant cytotoxicity after 3 days compared to air controls. Further, both Posh and third-generation e-cig Crème Brûlée flavored-aerosols elicited significantly increased ROS plus high levels of 8-isoprostane after 1 and 3 days compared to air controls, indicating increased oxidative stress. Posh and third-generation e-cig Crème Brûlée flavored-aerosols elicited reduction in NO levels after one day, but elicited increase in NO after 3 days. Genes in common dysregulated by both devices after 1 day included α7nAChR, Cyp1a1, Ahr, Mmp12, and iNos.

Conclusion

Our results suggest that ENDS Menthol and Crème Brûlée-flavored aerosol exposures from both 3rd- and 4th-generation ENDS devices are cytotoxic to macrophages and cause oxidative stress. This can translate into macrophage dysfunction. Although 4th-generation disposable ENDS devices have no adjustable operational settings and are considered low-powered ENDS devices, their aerosols can induce cellular toxicity compared to air-exposed control cells. This study provides scientific evidence for regulation of nicotine salt-based disposable ENDS products.

Understanding Factors Associated with Motivation to Quit Vaping among Vapers in the Federal Territory of Kuala Lumpur, Malaysia

The prevalence of vaping worldwide is showing an upward trend. This study aimed to determine the factors associated with motivation to quit vaping among vapers in the Federal Territory of Kuala Lumpur, Malaysia, through a cross-sectional, purposive sampling study. Respondents were required to complete a questionnaire consisting of vapers' sociodemographic questions, habitual behavioral pattern questions, the e-Fagerström Test of Nicotine Dependence, the Glover-Nilsson Smoking Behavioral Dependence Questionnaire, perception questions, motivation to quit questions, and withdrawal symptom questions. A total of 311 vapers participated in this study. The majority of the vapers were male (84.6%), younger (18-25 years) (55.3%), and with monthly income less than RM 4000 (USD 868; 83.9%). The level of motivation to quit vaping was found to have a significant association with the perception of vaping being as satisfying as cigarette smoking (p = 0.006) and mild to very strong nicotine dependence (p = 0.001). Participants who recorded moderate and strong habitual vaping behaviors had lower odds of having high motivation to quit vaping compared to those recording slight habitual behaviors (OR = 0.279, 95%CI(0.110-0.708), p = 0.007 and OR = 0.185, 95%CI(0.052-0.654), p = 0.009, respectively). Factors associated with higher motivation to quit vaping could be explored to gain better understanding of how to increase their motivation level for future quit attempts.

Biomarkers of Electronic Nicotine Delivery Systems (ENDS) Use

This perspective summarizes available evidence on biomarkers of exposure in electronic nicotine delivery system (ENDS) users to aid the overall assessment of the health consequences of using ENDS. Identification of novel biomarkers of exposure specific to ENDS use remains challenging because chemicals emitted from ENDS devices have many familiar sources. The biomarker levels of many tobacco-related toxicants measured in biological samples collected from ENDS users did not differ significantly from non-users, except for nicotine metabolites and a small number of biomarkers of exposure to volatile organic compounds and tobacco-specific tobacco nitrosamines. Several studies have shown that while exposed to nicotine, long-term exclusive ENDS users showed significantly lower levels of toxicant biomarkers than cigarette smokers. Studies have also shown that concurrent users of ENDS and combustible cigarettes ('dual users') are not reducing overall exposure to harmful toxicants compared to exclusive cigarette smokers. Because of an absence of validated ENDS-specific biomarkers, we recommend combining several biomarkers to differentiate tobacco product user groups in population-based studies and monitor ENDS compliance in randomized controlled trials. Using a panel of biomarkers would provide a better understanding of health effects related to ENDS use.

Critical Review of the Recent Literature on Organic Byproducts in E-Cigarette Aerosol Emissions

We review the literature on laboratory studies quantifying the production of potentially toxic organic byproducts (carbonyls, carbon monoxide, free radicals and some nontargeted compounds) in e-cigarette (EC) aerosol emissions, focusing on the consistency between their experimental design and a realistic usage of the devices, as determined by the power ranges of an optimal regime fulfilling a thermodynamically efficient process of aerosol generation that avoids overheating and "dry puffs". The majority of the reviewed studies failed in various degrees to comply with this consistency criterion or supplied insufficient information to verify it. Consequently, most of the experimental outcomes and risk assessments are either partially or totally unreliable and/or of various degrees of questionable relevance to end users. Studies testing the devices under reasonable approximation to realistic conditions detected levels of all organic byproducts that are either negligible or orders of magnitude lower than in tobacco smoke. Our review reinforces the pressing need to update and improve current laboratory standards by an appropriate selection of testing parameters and the logistical incorporation of end users in the experimental design.

A Critical Review of Recent Literature on Metal Contents in E-Cigarette Aerosol

The inhalation of metallic compounds in e-cigarette (EC) aerosol emissions presents legitimate concerns of potential harms for users. We provide a critical review of laboratory studies published after 2017 on metal contents in EC aerosol, focusing on the consistency between their experimental design, real life device usage and appropriate evaluation of exposure risks. All experiments reporting levels above toxicological markers for some metals (e.g., nickel, lead, copper, manganese) exhibited the following experimental flaws: (i) high powered sub-ohm tank devices tested by means of puffing protocols whose airflows and puff volumes are conceived and appropriate for low powered devices; this testing necessarily involves overheating conditions that favor the production of toxicants and generate aerosols that are likely repellent to human users; (ii) miscalculation of exposure levels from experimental outcomes; (iii) pods and tank devices acquired months and years before the experiments, so that corrosion effects cannot be ruled out; (iv) failure to disclose important information on the characteristics of pods and tank devices, on the experimental methodology and on the resulting outcomes, thus hindering the interpretation of results and the possibility of replication. In general, low powered devices tested without these shortcomings produced metal exposure levels well below strict reference toxicological markers. We believe this review provides useful guidelines for a more objective risk assessment of EC aerosol emissions and signals the necessity to upgrade current laboratory testing standards.

Exhalation of alternative tobacco product aerosols differs from cigarette smoke-and may lead to alternative health risks

BACKGROUND

Variation in alternative tobacco product (ATP) constituents, heating potential, and consumer behaviors have made it difficult to characterize their health risks. To date, most toxicity studies of ATPs have used established cigarette endpoints to inform study design. Furthermore, to assess where ATPs fall on the tobacco harm continuum, with cigarettes representing maximum potential risk, studies have tended to compare the relative biological responses to ATPs against those due to cigarettes.

OBJECTIVES

1) To characterize the exhalation profiles of two popular ATPs: electronic cigarettes (e-cigarettes) and hookah waterpipes (hookah) and 2) to determine if ATP exhalation patterns were representative of cigarette exhalation patterns.

METHODS

Exhalation patterns were recorded (mouth only, nose only, or both mouth and nose) among individuals observed in the New York City tri-state area using a recognizable tobacco product (cigarette, e-cigarette, or hookah). Cigarette smokers and e-cigarette vapers were observed on city streets; water-pipe smokers were observed inside Manhattan hookah bars.

RESULTS

E-cigarette vapers practiced exclusive nasal exhalation at far higher rates than did cigarette smokers (19.5% vs 4.9%). Among vapers, e-cigarette device type was also significantly associated with exhalation profile. Overall, cigarette smokers exhaled from their nose approximately half to one-third as often as ATP users (hookah and e-cigarettes, respectively).

CONCLUSIONS

Nasal exhalation of tobacco emissions appears to be a shared characteristic across several types of ATPs. It is therefore plausible that ATP-specific consumer behaviors may foster unique upper respiratory health consequences that have not been observed in smokers. Thus, product-specific behaviors should inform the prioritization of biological endpoints used in studies evaluating ATP toxicity and health effects.

Carcinogen Biomarkers in the Urine of Electronic Cigarette Users and Implications for the Development of Bladder Cancer: A Systematic Review

CONTEXT

Use of electronic cigarettes (e-cigarettes) has rapidly increased despite unclear longitudinal health effects. Once thought to be a safer alternative to tobacco smoke, it is possible that e-cigarettes expose the user to similar carcinogenic byproducts during the vaping process. These toxicants are metabolized and excreted in the urine, and may have oncogenic implications for bladder urothelium.

OBJECTIVE

To characterize and summarize known urinary carcinogenic biomarkers in e-cigarette users as they relate to the risk of developing bladder cancer.

EVIDENCE ACQUISITION

A systematic literature search was performed using the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) guidelines, and included PubMed, Embase, Web of Science, and Cochrane Central Register of Controlled Trials (CENTRAL). Relevant articles published in peer-reviewed journals, through January 2019, that reported on urinary biomarkers in e-cigarettes users were included. Parent compounds and urinary biomarkers were classified according to the International Agency for Research on Cancer Monographs on the Evaluation of Carcinogenic Risks to Humans and cross referenced using the Collaborative on Health and the Environment, Toxicant and Disease Database to determine a link to bladder cancer, grouped by strength of evidence.

EVIDENCE SYNTHESIS

Our initial search identified 1385 articles, 22 of which met final inclusion criteria and were included for analysis. In summation, these studies described 40 different parent compounds and four metals found in the urine of e-cigarette users. Since each parent compound can be metabolized several different ways, 63 unique toxicant or carcinogenic metabolite biomarkers were identified. Compared with nonuser controls, e-cigarette users had higher concentrations of urinary biomarkers of several carcinogenic compounds linked to bladder cancer. The majority of studies were limited by heterogeneous reporting and a dearth of control individuals who had never smoked.

CONCLUSIONS

Biomarkers of carcinogens, several with a strong link to bladder cancer, are present in the urine of e-cigarette users. Long-term implications of urothelial exposure to these toxicants are unknown but concerning, given the similarities to tobacco smoke and its established relationship with bladder cancer. Further study on the urological safety of e-cigarettes is necessary.

PATIENT SUMMARY

Our review shows that several carcinogens that have a known link to bladder cancer are present in the urine of electronic cigarette (e-cigarette) users. Further study on the urological safety of e-cigarettes is necessary.

Comparative Effects of E-Cigarette Aerosol on Periodontium of Periodontitis Patients

Introduction: Tobacco use is one of the main causes of periodontitis. E-cigarette are gaining in popularity, and studies are needed to better understand the impact of e-cigarettes on oral health. Objective: To perform a longitudinal study to evaluate the adverse effects of e-cigarettes on periodontal health. Methods: Naïve E-cigarette users, cigarette smokers, and non-smokers were recruited using newspaper and social media. Age, gender, and ethnicity, were recorded. Participants were scheduled for two visits 6 months apart. At each visit, we collected data on the frequency and magnitude of e-cigarette and cigarette use, and alcohol consumption. Carbon monoxide (CO) levels, cotinine levels, salivary flow rate, periodontal probing depth (PD), bleeding on probing (BoP), and clinical attachment loss (CAL) were also determined at both baseline and follow-up visits and compared between groups with two-way repeated measures ANOVA. Periodontal diagnosis and other categorical variables were compared between groups with the chi-square statistic and logistic regression. Results: We screened 159 subjects and recruited 119 subjects. One-hundred-one subjects (31 cigarette smokers, 32 e-cigarette smokers, and 38 non-smokers) completed every assessment in both visits. The retention and compliance rate of subjects was 84.9%. The use of social media and craigslist was significant in recruiting e-cigarette subjects. Ethnicity and race differed between groups, as did average age in the male subjects. Carbon monoxide and salivary cotinine levels were highest among cigarette smokers. Bleeding on probing and average PDs similarly increased over time in all three groups, but CAL uniquely increased in e-cigarette smokers. Rates of severe periodontal disease were higher in cigarette smokers and e-cigarette users than non-smokers, but interpretation is confounded by the older age of the cigarette smokers. Conclusion: Among the recruited participants, CAL after 6 months was significantly worse only in the e-cigarette smokers. This study design and protocol will assist in future larger studies on e-cigarette and oral health.

The Time Course of Compensatory Puffing With an Electronic Cigarette: Secondary Analysis of Real-World Puffing Data With High and Low Nicotine Concentration Under Fixed and Adjustable Power Settings

INTRODUCTION

In a secondary analysis of our published data demonstrating compensatory vaping behavior (increased puff number, puff duration, and device power) with e-cigarettes refilled with low versus high nicotine concentration e-liquid, here we examine 5-day time course over which compensatory behavior occurs under fixed and adjustable power settings.

AIMS AND METHODS

Nineteen experienced vapers (37.90 ± 10.66 years, eight females) vaped ad libitum for 5 consecutive days under four counterbalanced conditions (ie, 20 days in total): (1) low nicotine (6 mg/mL)/fixed power (4.0 V/10 W); (2) low nicotine/adjustable power; (3) high nicotine (18 mg/mL)/fixed power; (4) high nicotine/adjustable power (at 1.6 Ohm). Puff number, puff duration, and power settings were recorded by the device. For each day, total daily puffing time was calculated by multiplying daily puff number by mean daily puff duration.

RESULTS

A significant day × setting interaction revealed that whilst puffing compensation (daily puffing time) continued to increase over 5 days under fixed power, it remained stable when power settings were adjustable. Separate analysis for puff number and puff duration suggested that the puffing compensatory behavior was largely maintained via longer puff duration.

CONCLUSIONS

Under fixed power conditions (4.0 V/10 W), vapers appear to compensate for poor nicotine delivery by taking longer puffs and this compensatory puffing appears to be maintained over time.

IMPLICATIONS

Studies in smokers suggest that when switching to lower nicotine levels, compensation for poorer nicotine delivery is transient. Our novel findings suggest that vapers show a different pattern of compensation which is influenced by both nicotine strength and device power settings. When power is fixed (4.0 V; 10 W), compensation (via more intensive puffing) appears prolonged, persisting up to 5 days. Under adjustable settings when power is increased, puffing patterns remain stable over time. Implications of such compensatory behaviors for product safety and user satisfaction need further exploration.

E-cigarette Use in Prisons With Recently Established Smokefree Policies: A Qualitative Interview Study With People in Custody in Scotland

INTRODUCTION

E-cigarettes were one measure introduced to help people in custody (PiC) to prepare for and cope with implementation of comprehensive smokefree policies in Scottish prisons. Our earlier study explored experiences of vaping when e-cigarettes were first introduced and most participants were dual tobacco and e-cigarette users. Here we present findings of a subsequent study of vaping among a different sample of PiC when use of tobacco was prohibited in prison, and smokefree policy had become the norm.

METHODS

Twenty-eight qualitative interviews were conducted with PiC who were current or former users of e-cigarettes in prison, 6-10 months after implementation of a smokefree policy. Data were managed and analyzed using the framework approach.

RESULTS

PiC reported that vaping helped with mandated smoking abstinence. However, findings suggest that some PiC may be susceptible to heavy e-cigarette use potentially as a consequence of high nicotine dependence and situational factors such as e-cigarette product choice and availability in prisons; issues with nicotine delivery; prison regimes; and use of e-cigarettes for managing negative emotions. These factors may act as barriers to cutting down or stopping use of e-cigarettes by PiC who want to make changes due to dissatisfaction with vaping or lack of interest in continued use of nicotine, cost, and/or health concerns.

CONCLUSIONS

E-cigarettes helped PiC to cope with smokefree rules, although concerns about e-cigarette efficacy, cost, and safety were raised. PiC may desire or benefit both from conventional smoking cessation programs and from interventions to support reduction, or cessation, of vaping.

IMPLICATIONS

Findings highlight successes, challenges, and potential solutions in respect of use of e-cigarettes to cope with mandated smoking abstinence in populations with high smoking prevalence and heavy nicotine dependence. Experiences from prisons in Scotland may be of particular interest to health and/or justice services in other jurisdictions, with similar legislation on e-cigarettes to the United Kingdom, who are planning for institutional smokefree policies in their prisons or inpatient mental health settings in the future.

E-cigarettes compromise the gut barrier and trigger inflammation

E-cigarette usage continues to rise, yet the safety of e-cigarette aerosols is questioned. Using murine models of acute and chronic e-cigarette aerosol inhalation, murine colon transcriptomics, and murine and human gut-derived organoids in co-culture models, we assessed the effects of e-cigarette use on the gut barrier. Histologic and transcriptome analyses revealed that chronic, but not acute, nicotine-free e-cigarette use increased inflammation and reduced expression of tight junction (TJ) markers. Exposure of murine and human enteroid-derived monolayers (EDMs) to nicotine-free e-cigarette aerosols alone or in co-culture with bacteria also causes barrier disruption, downregulation of TJ protein, and enhanced inflammation in response to infection. These data highlight the harmful effects of "non-nicotine" component of e-cigarettes on the gut barrier. Considering the importance of an intact gut barrier for host fitness and the impact of gut mucosal inflammation on a multitude of chronic diseases, these findings are broadly relevant to both medicine and public health.

E-cigarettes compromise the gut barrier and trigger inflammation

E-cigarette usage continues to rise, yet the safety of e-cigarette aerosols is questioned. Using murine models of acute and chronic e-cigarette aerosol inhalation, murine colon transcriptomics, and murine and human gut-derived organoids in co-culture models, we assessed the effects of e-cigarette use on the gut barrier. Histologic and transcriptome analyses revealed that chronic, but not acute, nicotine-free e-cigarette use increased inflammation and reduced expression of tight junction (TJ) markers. Exposure of murine and human enteroid-derived monolayers (EDMs) to nicotine-free e-cigarette aerosols alone or in co-culture with bacteria also causes barrier disruption, downregulation of TJ protein, and enhanced inflammation in response to infection. These data highlight the harmful effects of "non-nicotine" component of e-cigarettes on the gut barrier. Considering the importance of an intact gut barrier for host fitness and the impact of gut mucosal inflammation on a multitude of chronic diseases, these findings are broadly relevant to both medicine and public health.

Daily exposure to formaldehyde and acetaldehyde and potential health risk associated with use of high and low nicotine e-liquid concentrations

Recent evidence suggests that e-cigarette users tend to change their puffing behaviors when using e-liquids with reduced nicotine concentrations by taking longer and more frequent puffs. Using puffing regimens modelled on puffing topography data from 19 experienced e-cigarette users who switched between 18 and 6 mg/mL e-liquids with and without power adjustments, differences in daily exposure to carbonyl compounds and estimated changes in cancer risk were assessed by production of aerosols generated using a smoking machine and analyzed using gas and liquid chromatography. Significant differences across conditions were found for formaldehyde and acetaldehyde (p < 0.01). Switching from a higher to a lower nicotine concentration was associated with greater exposure regardless of whether power settings were fixed or adjustable which is likely due to increased liquid consumption under lower nicotine concentration settings. Daily exposure for formaldehyde and acetaldehyde was higher for 17/19 participants when using low (6 mg/mL) compared with high (18 mg/mL) nicotine e-liquid concentration when power was fixed. When power adjustments were permitted, formaldehyde and acetaldehyde levels were higher respectively for 16/19 and 14/19 participants with the use of 6 compared with 18 mg/mL nicotine e-liquid.

Use of social media to establish vapers puffing behaviour: Findings and implications for laboratory evaluation of e-cigarette emissions

The recent growth in e-cigarette use has presented many challenges to Public Health research, including understanding the potential for e-cigarettes to generate toxic aerosol constituents during use. Recent research has established that the way e-cigarettes are puffed influences the magnitude of emissions from these devices, with puff duration the dominant driving force. Standardised puffing machine methods are being developed to harmonise testing approaches across laboratories, but critical to their success is the degree with which they accurately reflect vapers real-world puffing behaviours (topography). Relatively limited data is available examining the way vapers puff, with significant inconsistencies between studies. Here we report the creation and analysis of a large database of public-domain vaping videos to establish e-cigarettes puffing behaviour in near natural settings. Over 300 videos containing 1200 puffing events from 252 vapers were obtained from social media sources, divided approximately equally amongst cigalike, Ego and Advanced Personal Vapouriser ("APV", also referred to as "boxmod") types of e-cigarettes. Analysis showed that similar mean puff durations were found for all three categories of vaping devices. This includes direct-to-lung as well as mouth-to-lung puffing behaviours. A 3 s puff duration, as used in the recently published ISO puffing standard ISO 20,768:2018, appears appropriate for average behaviours. However, the wide diversity of puffing durations observed amongst vapers means it may be challenging to identify a simple yet comprehensively representative single machine-puffing regimen for laboratory studies. A puff duration of around 5.6 s appears to represent 95th percentile puffing behaviours amongst vapers and may be an appropriate choice for scientists and regulators seeking an additional more intense puffing regime. A range of new behavioural patterns have been identified whose impact on aerosol exposure need to be considered. Public-domain video records of vapers provides valuable and accessible insights into real-world use behaviours. It is freely available, and constantly updated with new material, and therefore provides a valuable resource for scientists seeking to understand real-world vaping behaviours.

'Real-world' compensatory behaviour with low nicotine concentration e-liquid: subjective effects and nicotine, acrolein and formaldehyde exposure

AIMS

To compare the effects of (i) high versus low nicotine concentration e-liquid, (ii) fixed versus adjustable power and (iii) the interaction between the two on: (a) vaping behaviour, (b) subjective effects, (c) nicotine intake and (d) exposure to acrolein and formaldehyde in e-cigarette users vaping in their everyday setting.

DESIGN

Counterbalanced, repeated measures with four conditions: (i) low nicotine (6 mg/ml)/fixed power; (ii) low nicotine/adjustable power; (iii) high nicotine (18 mg/ml)/fixed power; and (iv) high nicotine/adjustable power.

SETTING

London and the South East, England.

PARTICIPANTS

Twenty experienced e-cigarette users (recruited between September 2016 and February 2017) vaped ad libitum using an eVic Supreme™ with a 'Nautilus Aspire' tank over 4 weeks (1 week per condition).

MEASUREMENTS

Puffing patterns [daily puff number (PN), puff duration (PD), interpuff interval (IPI)], ml of e-liquid consumed, changes to power (where permitted) and subjective effects (urge to vape, nicotine withdrawal symptoms) were measured in each condition. Nicotine intake was measured via salivary cotinine. 3-Hydroxypropylmercapturic acid (3-HPMA), a metabolite of the toxicant acrolein, and formate, a metabolite of the carcinogen formaldehyde, were measured in urine.

FINDINGS

There was a significant nicotine concentration × power interaction for PD (P < 0.01). PD was longer with low nicotine/fixed power compared with (i) high nicotine/fixed power (P < 0.001) and (ii) low nicotine/adjustable power (P < 0.01). PN and liquid consumed were higher in the low versus high nicotine condition (main effect of nicotine, P < 0.05). Urge to vape and withdrawal symptoms were lower, and nicotine intake was higher, in the high nicotine condition (main effects of nicotine: P < 0.01). While acrolein levels did not differ, there was a significant nicotine × power interaction for formaldehyde (P < 0.05).

CONCLUSIONS

Use of a lower nicotine concentration e-liquid may be associated with compensatory behaviour (e.g. higher number and duration of puffs) and increases in negative affect, urge to vape and formaldehyde exposure.